“Mysterious” plane circling over Denver was “just” an E-6B Mercury “doomsday” plane

Photos and video of a “mysterious” plane circling over Denver are making the rounds. But the aircraft was “just” a U.S. Navy Doomsday plane.

On Nov. 16 people in the Denver metropolitan area saw a white, four-engined aircraft performing a racetrack for several times over Colorado before heading to Oklahoma. The aircraft could be tracked online on Flightradar24 by means of ADS-B using callsign Iron 99.



Even though some media outlets published some funny articles with headlines referring to a “mystery flight” or a “mysterious plane” there is really little mystery around that aircraft: it was an E-6B Mercury.

The use of “Iron 99” is also pretty standard: Iron is one of the radio callsigns of the VQ-3 “Ironmen”, a naval aviation squadron of the United States Navy based at Tinker Air Force Base, Oklahoma (incidentally, where the aircraft headed after orbiting over Denver….)

Built on the Boeing 707 airframe and using a B737 cockpit, the E-6B aircraft has a range of 5,500 miles, and accommodates 23 crew members.


The U.S. Navy has a total fleet of sixteen E-6B Mercury (TACAMO – “TAke Charge And Move Out”) that play an extremely important role for U.S. National Security: they are used to relay instructions to the fleet ballistic missile submarines in case of nuclear war but also act as back ups of the four E-4Bs NAOC (National Alternate Operations Center), working as ABNCP (Airborne Command Post) platforms (hence “Doomsday Plane“).

They are often trackable online, while performing various critical missions: the so-called Looking Glass mission (mirroring the ground-based C3 center at Offutt AFB and relaying orders); talking to submarines trailing a 26,000 ft wire antenna; launching commands to ICBMs (InterContinental Ballistic Missiles) via Airborne Launch Control System, and performing C3 (Command Control Communication) operations to forces operating in theater or to the U.S. strategic bombers flying Global Strike missions.

The Mercury is capable to communicate on virtually every radio frequency band, on commercial satellites and on the Internet, using also a secure VOIP system. This aircraft usually operates flying orbits/circles while trailing their antennas or to exploit a particular geostationary satellite for radio comms.

Noteworthy, on Aug. 27, the E-6B 163918 used the very same callsign Iron 99.

Screenshot from Global ADSB Exchange showing E-6B using callsign Iron 99 on Aug. 27, 2016
Screenshot from Global ADSB Exchange showing E-6B using callsign Iron 99 on Aug. 27, 2016

Interestingly, on Mar. 8, 2016 an E-6B 162784 used the callsign “Trump” for the first time.

Top image credit: screenshot from ABC. Rest of images: screenshots from Flightradar24.com


About David Cenciotti
David Cenciotti is a journalist based in Rome, Italy. He is the Founder and Editor of “The Aviationist”, one of the world’s most famous and read military aviation blogs. Since 1996, he has written for major worldwide magazines, including Air Forces Monthly, Combat Aircraft, and many others, covering aviation, defense, war, industry, intelligence, crime and cyberwar. He has reported from the U.S., Europe, Australia and Syria, and flown several combat planes with different air forces. He is a former 2nd Lt. of the Italian Air Force, a private pilot and a graduate in Computer Engineering. He has written five books and contributed to many more ones.


  1. You can heard these aircraft from time to time on 8.992 MHz USB, typically reading out a coded message. My hunch is they’re ordering pizza to be ready when they land.

  2. It was an E6B. It was not called IRON99 though. The news media uses a website called flightradar24 to “see” a/c above. Flightradar24 primarily uses adsb technology to track a/c. Most military a/c do not have adsb transponders that transmit a/c identification (among other things.). Flightrada24 incorrectly “tagged” this flight as IRON99 and tracked it using raw radar data. When the media started calling (the wrong people, by the way) asking for info on IRON99 nobody knew what they were talking about. As for its mission? Well, perhaps it was in support of a routine large force training exercise taking place out of Ellsworth AFB to the north. Rest assured that the a/c was always in radar and radio contact with the FAA/ATC and there was nothing unusual about this flight whatsoever.

    • Saying it was always in radio contact with the FAA is disregarding the fact that no one at the FAA knew anything about the flight.

      • I actually am an Air Traffic Controller and have access to FAA radar and radio replay equipment. I watched the replay of this event. It was there, the FAA knew about it and it was in contact with ATC. We aren’t in the business of asking military (or any a/c for that matter) what the nature of their business in the sky is. My point in my comment was to explain why there was confusion. The news media was asking about a specific callsign of an a/c over Denver. The callsign they asked about was not associated with any a/c over Denver at the time. At first, the journalists called the wrong ATC facility anyway. When they called the high altitude ATC facility, they were still using the wrong callsign, so the answer they received was “There is no IRON99”.

      • I’m not exactly sure what your comment implies. No one at the Denver ARTCC (the air traffic control facility that has jurisdiction over this airspace) could give the journalist on the phone any info on IRON99. The simple reason for that is because this aircraft was not using the callsign IRON99. (I stayed all of this above)
        Why am I so certain of myself? I work at Denver ARTCC as a controller and watched the radar replay of the event the following day!
        As for the reason it was there?… Well, it’s not ATC’s business to know the reason for every aircraft to be in the air. We just keep them separated. I did however offer some guess as to its mission in my original post.

  3. This plane usually doesn’t make such public displays. Make no mistake – this is signal to Russia.

    • Oh my. Leroy and his propaganda posts. Why should that be a signal to Russia if a Navy plane is flying over the US? By that logic any Tu-214 that is flying over Russia is a signal to the US. *facepalm*

      Could also be a signal to Santa Clause.

      • Boy are you a dumb bast …. uninformed. Since you don’t know this plane’s mission and its normal flight profile (I do) I’ll just quote the article and see if you have enough brainpower to figure it out:

        … the so-called Looking Glass mission (mirroring the ground-based C3 center at Offutt AFB and relaying orders); talking to submarines trailing a 26,000 ft wire antenna; launching commands to ICBMs (InterContinental Ballistic Missiles) via Airborne Launch Control System…”.

        Suffice it to say you are way out of your league. Totally lacking in Navy flight experience. This was an unambiguous message to Russia. At least to people in Russia who understand what the message was because of how and why it was sent. But to you? May as well have been a Chinese speaking mandarin to a chimp. &Guess what? Regarding this matter, me Chinese, you chimp! In this, and everything else aviation. Want a banana?

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